index.js

'use strict'
const Task = require('data.task')
const Spotify = require('./spotify')
const {List} = require('immutable-ext')
const {Pair, Sum} = require('./monoid')
const Intersection = require('./monoids/intersection')

const argv = new Task((rej, res) => res(process.argv))
const names = argv.map(args => args.slice(2))


const related = name =>
  Spotify.findArtist(name)
  .map(artist => artist.id)
  .chain(Spotify.relatedArtists)
  .map(artists => artists.map(artist => artist.name))

const artistIntersection = rels =>
  rels
  .foldMap(x => Pair(Intersection(x), Sum(x.length)))
  .bimap(x => x.xs, y => y.x)
  .toList()

const main = names =>
  List(names)
  .traverse(Task.of, related)
  .map(artistIntersection)

names.chain(main).fork(console.error, console.log)